Process of producing dicarboxylic acid anhydrides



June 21, 1949.

Filed May 30, 1945 lv .f c

June 21, 1949. l. E. Lr-:vlNE ETAL PROCESS OF PRODUGING DICARBOXYLIC ACID ANHYDRIDES 'Filed May 30, 1945 3 Sheets-Sheet 2 June 21, 1949.

PROCESS OF PRODUCING DICARBOXYLIC ACID ANHYDRIDES Filed May 50, 1945 RECYCZE RECVCZE l. E. LEVINE ETAL 3 Sheets-Sheet 3 Patented June 21, 1949 PROCESS OF PRODUCING DICARBOXYLIC ACID ANHYDRIDES Irving E. Levine and william n. examen, Berkeley, Calif., asslgnors to Caliirnlaglt'csearch Corporation, San Francisco, Calif., a corpora.-

tion of Delaware Application May so, 194s, serial-Ng. 596,646

K Clalms.

l This invention relates to the production of dicarboxylic acidv anhydrides, and, more particularly, to a process for obtaining phthalic anhydride from a mineral oil or petroleum fraction or from hydrocarbon mixtures of similar complexity. l

It is known that phthalic anhydride may be produced by vapor phase catalytic oxidation of naphthalene at relatively high temperatures. Vapor phase catalytic oxidation of petroleum hydrocarbons to produce phthalic anhydride also has been proposed, but the yields obtained in the proposed processes have been so low or the Waste of valuable hydrocarbons in the oxidation has been so great that production of phthalic anhydride from petroleum or similar complex hydrocarbon mixtures appears to have been discarded as impracticable'.

Excessive waste of hydrocarbons in the production of phthalic anhydride by vapor phase oxidation of petroleum hydrocarbon mixtures (Cl. 26o-342) .A

stantlally entirely cl2-,compounds which are not convertible by directy oxidation to said anhydride.-

Another object'of the invention is to derive vphthalic anhydride or the like (by a process inoxidized in vaporphas'e at high temperature.

has, in the past, not been avoided because alarge proportion of the hydrocarbons in the mixture was not convertible by direct oxidation to the desired anhydride, but was destroyed or lost by combustion and discarded as Waste gas.

Further, it was generally recognized that those petrole-um hydrocarbons (hereinafter termed anhydride inconvertible hydrocarbons) not convertible by direct oxidation to phthalic anhydride, were very dimcult or in some cases even virtually impossible to separate from the desired hydrocarbons (hereinafter termed anhydride convertible hydrocarbons) which might be directly oxidized to phthalic anhydride. It was therefore thought that formation of constant boiling mixtures, etc., precluded a practical or economical separation of these anhydride convertible and anhydride inconvertible components.

Accordingly, -'the preparation of phthalic anhydride from petroleum fractions containing large proportions of inconvertible hydrocarbons appears to have been discarded by prior workers as impracticable for the foregoing or other reasons. At least such prior processes have not been found commercially practicable heretofore.

An object of the invention is to provide a process for deriving phthalic anhydride or the like from a hydrocarbon mixture containing a relatively large proportion of, or even consisting sub- A iur-ther object of the invention is to increase the over-all yield of useful products in a process involving the conversion to phthalic anhydridelof av mixture of hydrocarbons, at least aboutv 40% of which, land usually more than about by weight, are not convertible to saidv anhydride by direct catalytic oxidation.

Another object of the invention is the production of dicarboxylic acids such as phthalic anhydride from cyclo-aliphatichydrocarbons.

A further object of the invention comprises the production of aryl dicarboxylic acid anhydrides from parafllnic hydrocarbons.

An additional object is to provide a process for producing an improved blending stock for aviation gasoline, together with phthalic anhydride, from an equilibrium mixture of aromatizedpetroleum hydrocarbons, said equilibrium mixture boiling within the range of from about 230 F. to

about 320 F., and preferably from approximately 275 to 295 F.

A still further object of the invention is to provide a process of separating phthalic anhydride inconvertible aromatic hydrocarbons from phthalic anhydride convertible aromatic hydrocarbons in mixtures derived from petroleum whereby economic conversion to and purication of phthalic anhydride may be obtained.

Briefly described, a process embodying the principles of this invention comprises the steps of t (l) Aromatizing a petroleum fraction or the like to yield a reaction mixture of anhydride convertible and phthalic anhydride'inconvertible hydrocarbons comprising aromatic compounds and usually also containing non-aromatic compounds,

(2) Initially separating out of said reaction mixture an aromatic fraction consisting at least predominantly of a mixture of phthalic anhydride .inconvertible with a minor proportion of phthalic fraction non-destructively to obtain mixed alkyl Feed stocks Various hydrocarbon'lmixture's maybe utilized'l as an aromatization feed stock in accordance with the principles of this invention. Naphthenic hydrocarbon mixtures from naphthene type petroleum crude oils comprise onevpreferred type ofV feed stock. Such mixtures are normally termed "straight run distillates in the petroleum industry. The hydrocarbons present in this preferred feed stock are substantially anhydride inconvertible and are believed to consist largely of cyclo-aliphatic hydrocarbons with six carbon atoms in the cyclo-aliphatic ring and with aliphatic side chains attached to the ring. Some ve and seven carbon atom cyclo-aliphatic rings may l be present.` Both the number of side chainsl and the length of each chain attached to the foregoing rings varies among the many compounds normally present in a petroleum hydrocarbon mixture. In general, these variables are a function of the average molecular weight or more particularly the 1 boiling range and distillation curve of the petroleum fraction selected. A vnaphthenic hydrocarbon mixture consisting essentially of hydrocarbons having from six to twelve carbon atoms in the molecule and preferably composed at least predominantly of hydrocarbons containing from seven to eight carbon atoms at present is regarded as a most desirable feed stock. One such feed stock may be obtained by fractional distillation of a naphthenic petroleum from Kettleman Hills oil field in California. Other sources of napthenic petroleums are, of course, suitable. The fraction selected desirably should boil within the range of from about 180 to 420 F. and preferably from about 180 to 320 F. In some instances an even more narrow cut boiling from 230 to 275 F. is preferred. 'Ihe .selection of feed stock is important since its composition affects subsequent process steps which are correlated therewith.

Aromariarztion.I 1

As previously set forth an initial step in the exemplary process comprises aromatization of the particular petroleum feed stock selected. Where the above naphthenic hydrocarbon mixture is utilized, the aromatization step comprises conversion of naphthenic hydrocarbons to. aromatic hydrocarbons. The conversion of hydrocarbons to aromatics in such processes is believed to occur by dehydrogenation of the six carbon atom rings from cyclo-aliphatic to aromatic while leaving alkyl groups attached to the residual nucleus, for example:

3H: C Hl Isomerizaton of any C1 alicyclic rings present .and dehydrogenation to aromatic compounds also is believed to occur. Likewise Cs alicyclic rings containing side chains are converted to aromatics by isomerization and dehydrogenation.

. various reactions represent an over-simplification of the aromatization reactions which may actually occur since de-alkylation and shortening of side chains as by cracking undoubtedly take place. In any event, the aromatization reaction product comprises a complex mixture of phthalic anhydride inconvertible aromatics with a minor proportion of phthalic anhydride convertible aromatics and also may contain anhydride inconvertible non-aromatics such as-saturated or un saturated paraiilns and naphthenes. The overall complexity of the mixture and the relative proportion of the above-mentioned non-aromatic components depend upon the effectiveness of the particular aromatization process utilized as Well as upon the specific hydrocarbon feed stock selected.

Although a naphthenic straight-run petroleum fraction has been found more adaptable to the present preferred processes than other hydrocarbon mixtures, by adapting the aromatization stage of the process to the feed stock selected and making other suitable adjustments in subsequent process steps, as hereinafter explained, widely different types of hydrocarbon mixtures can be converted to phthalic anhydride or the like in conformance with the principles of the present invention. aromatic hydrocarbons together with naphthenic hydrocarbons or paraflinic hydrocarbons or both may be utilized. Likewise, highly paraflinic or olenic petroleum hydrocarbon mixtures are not precluded and aromatization thereof may be effected by known processes involving dehydrogenation and cyclization usually with at least some cracking.

Aromatization reactions of the foregoing parainic hydrocarbons (arranged in semi-ring form for illustrative purposes) are exemplified by the following:

These For example, mixtures containing various known processes may be utilized within the broader aspects of this invention and are embraced within the term aromatization" as used in the present specification and claims.

Eliminating interfering hydrocarbons from reaction mixture The aromatization stage of this process yields a reaction mixture which, as explained hereinabove, is largely phthalic anhydride inconvertible. Normally, at least a two-stage treatment is required to eliminate from this reaction mixture those hydrocarbons which tend to interfere with or would be wasted in the phthalic anhydride conversion stage. These two major treatments comprise:

(a) Initial separation-This stage involves elimination of non-aromatic hydrocarbons at least to the point of a minor proportion in the reaction mixture and separation of a highly aromatic fraction consisting essentially of an equilibrium mixture of phthalic anhydride inconvertible hydrocarbons with phthalic anhydride convertible hydrocarbons. The mixture resulting from this initial separation should contain no more than about 25%, and preferably less than about 15%, of non-aromatic hydrocarbons.

(b) Non-destructive separation of phthalic anhydride inconvertible aromatic hydrocarbons. The foregoing initial separation adapts the remaining hydrocarbon mixture to this stage of the process, wherein at least a major proportion of the phthalic anhydride inconvertible aromatic hydrocarbons are separated, without destruction, from the phthalic anhydride convertible aromatic hydrocarbons present in the mixture. A suitable and preferred method of treatment comprises super-fractionation of the mixed aromatic hydrocarbons (usually alkyl benzenes) in a distillation column. When this preferred method of separation is utilized, the fraction treated preferably should contain no more than about 15% of non-aromatic anhydride inconvertible hydrocarbons. Desirably the fraction to be treated in this stage should approach 90 to 100% aromatic content.

Initial separation stage-The initial separation (stage "a above) may, and usually does, require several process steps. Thus, a preferred procedure involves:

gasoline range and up to an end point of about.

275 F. from the foregoing residual liquid t0 leave a hydrocarbon fraction boiling above about 275 F.

(3) Separating from the above last heavier hydrocarbon mixture a fraction boiling within the range of from about 275 F. to about 295 F. by eliminating hydrocarbon components boiling above` about 295 F. The higher boiling hydrocarbons thus eliminated may be recycled to the aromatization zone when desired.

A fourth process step may be desirable, or even required, depending on the type and boiling range of the feed stock selected, as well as upon the effectiveness of the aromatization process utilized. It has been found that witha highly naphthenic or aromatic feed and a highly effective aromatization process, such as that hereinafter described, this fourth process step is unnecessary if the original feed to aromatization boils within the range of from about 180 to about 275 F., and preferably within the range of from about 230 to about 275 F. However, it also has been found that when other types of feed stock or wider boiling range feeds or substantially less effective aromatization processes are utilized, a. fourth process step is highly desirable, if not absolutely necessary, to adapt the resulting mixture to the second stage oi major treatment (i. e., to non-destructive separation of phthalic anhydride inconvertible aromatics from the 275 F. to 295 F. fraction).

(4) The fourth process step (in one sense optional) comprises reduction of non-aromatic hydrocarbon content to at least about 25% by weight, and preferably substantially complete elimination of non-aromatic hydrocarbons from the foregoing 275 to 295 F. fraction. This process step may be carried out by: (u.) selective solvent extraction processes, e. g., a selective solvent distillation method such as described in Cope et al.. Patent No. 2,215,915, issued September 24, 1940, or by (b) selective conversion of the non-aromatic hydrocarbons to lower boiling compounds, -as by selective cracking, or (c) preferably by subjecting the said 275 F. to 295 F. hydrocarbon fraction to a second aromatization treatment whereby the non-aromatic hydrocarbons' are converted either to aromatics or lower boiling hydrocarbons, or both. When this or a selective cracking treatment is utilized, new hydrocarbons boiling outside the selected range preferably should be eliminated as by fractional distillation.

The above fourth process step in the initial separation need not necessarily occur in the order indicated. Thus, non-aromatic hydrocarbon content may be reduced prior to step (3) and the desired 275 F. to 295 F. cut taken from the resulting more aromatic mixture.

The foregoing initial separation procedures yield a mixture of aromatic hydrocarbons containing phthalic anhydride convertible and phthalic anhydride inconvertible alkyl benzenes of the selectedp boiling range in substantially the proportion produced by the aromatization reaction. This fraction is, accordingly, vherein termed an equilibrium mixture of alkyl benzenes` or "equilibrium alkyl benzenes, and the -relative proportion of convertible and inconvertible alkyl benzenes is termed equilibriumproportions of alkyl benzenes to distinguish from equilibrium proportions Ainvolving other aromatic or lnon-aromatic hydrocarbons present in the over-allmixture from the aromatization reaction. 1 'I'his equilibrium mixture of alkyl benzenes of the selected boiling range is a valuable blending agent for aviation gasoline, but according to the present invention, the mixture is split into two components, each of which is 'given enhanced value, i. e., phthalic anhydride inconvertiblealkyl benzenes are separated to produce a mixture having still greater value as an aviation gasoline blending agent and to yield an alkyl benzene residue adapted to phthalic anhydride production.

Non-destructive separation, of phthalic anhydride inconvertible aromatic hydrocarbons 'The above described production of an equilibrium mixture of alkyl benzenes containing. no more than about 25% and preferably less than about of non-aromatic hydrocarbons is correlated With and particularly adapted to the nondestructive separation stage` of the present process. As previously indicated, this non-destructive separation is a difficult one, even with oom--A positions produced by the foregoing correlated process stages, and is preferably effected by super-fractionation in a distillation column.

Separation by super-fractionation requires a able separation. A preferred method of superfractionation is to operate the fractionating unit continuously at a given constant feed rate While (1) removing overhead distillate and bottoms at a constant ratio corresponding to the feed rate and in a relative proportion such that desired purity of the selected component may be maintained, and (2) maintaining a constant volume of liquid. of the still bottoms by controlling rate ofheat input thereto. Maintenance of the conz stant volume of bottoms may be eected, for example, by a constant level control which increases the amount of steam admitted tothe still heating' unit when the level' of still bottoms begins to raise and decreases steam input when the volume of bottoms begins to drop below the predetermined level.

At least a major proportion of the phthalic anhydride inconvertible alkyl benzenes are separated as overhead in the foregoing preferred super-fractionation and phthalicanhydride convertible alkyl benzenes are concentrated in the residue or still bottoms. Preferably all of the phthalic anhydride inconvertible components are not removed from the residue in the non-destructive stage. On the contrary, it has been found advantageous to eiect purification in tvs/'o stages, namely: (1) by non-destructive distillation as above described, and (2) by destructively eliminating residual impurities, as by selective oxidation or other chemical alteration, to facili tate separation of the reaction products.

In conformance with this preferred procedure,

a small pa'rt ofthe phthalic anhydride incon-f vertible hydrocarbons are retained in the residue from the non-destructive separation, so that the residue containsj from about 3% to 30%, morev parts convertible alkyl benzenes and about 1 to 4 parts inconvertible` hydrocarbons, which effects a non-destructive recovery of '16 to '79 out of 80 parts of the inconvertible components. The 1 to 4 parts inconvertiblecompounds remaining in the residue amount to from about 5% to about 17% of the phthalic anhydride convertible alkyl benzenes and can be eliminated destructively While serving a. useful purpose in the phthalic anhydride conversion, asdescribed hereinbelow.

Production of phthalic anhydride and diminution of inconvertible hydrocarbons i It has been discovered that relatively pure phthalic anhydride can be produced from mixtur'es of phthalic anhydride convertible and inconvertible alkyl benzenes, such as the foregoing, by vapor phase partial oxidation. Phthalic anhydride containing 1% or less percent aromatic impurities can be obtained in good yields from alkyl benzene residues containing'from 10% or less to about 30% inconvertible hydrocarbon impurities, 'even though these impurities be` alkyl benzenes, separable, if at all, only with great difiiculty by super-fractionation. These impurities A may be eliminated during phthalic anhydrideproduction stage by partial oxidation of the.

phthalic anhydride convertible alkyl benzenes and separation' of this reaction product. Initial purification preferably is obtained by destruci' tion, e. g., selective over-oxidation, of phthalic anhydride inconvertible hydrocarbons. It is pre-- ferred to utilize selective over-oxidation in the destruction of the phthalic anhydride inconvertible hydrocarbons, since these impurities'thereby serve the useful purpose of supplying heat to maintain and control reaction temperatures in the anhydride conversion lzone; i. e., heat of reaction is furnished at the expense of impurities rather than necessarily at the expense of phthalic anhydride convertible components, and the impurities are simultaneously converted to a reaction mixture which is easily 'separable from the phthalic anhydride produced.

In this stage of the preferred process, phthalic anhydride convertible alkyl benzenes are only partially oxidized and the reaction is stopped short of ring rupture and substantially at the'phthalic anhydride stage. Desirably in the same oxidation stage the phthalic anhydride inconvertible alkyl benzenes are selectively over-oxidized, at least to selective condensation or other suitable processes.

The foregoing partial oxidation and selective over-oxidation are carried out in accordance with this preferred embodiment of the invention by mixing the vaporized alkyl benzene vapors with an excess of an oxygen-containing gas, such as air, and contacting the vapor-oxygen mixture at elevated temperatures with a metal oxide which is an oxidation catalyst, such asa vanadium oxide catalyst. The reaction is exothermic and heat is removed by any suitable means to control the temperature of the reaction. Catalyst temperature preferably is maintained in the zone of red heat. Such relatively high temperatures, together with a large excess of the oxygen-containing gas, serves to form the phthalic anhydride quickly and to cause the phthalic anhydride inconvertible ring rupture, catalyst temperatures as low asV 800 F. are operable. However, a catalyst temperature in the dark red heat range is desirable, and from a dark blood red to a dark cherry red, as indicated in Marks Chemical Engineers Handbook (2nd ed.), page 297, is preferred (about 990 F. to 1175 F.) It should be clear that the entire catalyst bed need not be maintained at this high temperature level. Only a relatively short zone, suicient to insure selective over-oxidation at least to ring rupture and preferably to carbon dioxide and water, need be in the dark red heat range (e. g., 1/3 to 1A; of the catalyst bed). Likewise, it is to be understood that temperatures referred to above are catalyst temperatures as measured by a thermocouple in the catalyst bed.

To illustrate in detail processes embodying the principles of this invention and to guide those skilled in the art in the practice thereof, the following examples of processes and illustrative data are given:

In the drawing,

Figure 1 is a schematic flow diagram of the major process stages in an illustrative process.

Figure 2 is a ilow diagram illustrating a process utilizing a relatively narrow boiling range feed stock.

Figure 3 illustrates diagrammatically a process in which a wider boiling feed stock is utilized.

In Figure 1, the process represented comprises i'lve major steps, namely, aromatization, initial separation, super-fractionation, partial oxidation, and recovery of product.

Aromatization may be effected by any suitable process as previously indicated. However, a preferred process comprises passing a hydrocarbon feed such as petroleum naphtha consisting essentially of Ce and heavier hydrocarbons at from about 900 to about 1200 F., desirably about 1000 F., over a Vanadium oxide-alumina or molybdenum oxide-alumina catalyst. Space rate desirably is from about 0.1 to about 2.0 volumes of liquid hydrocarbon feed per volume of catalyst per hour, and it is preferred to maintain a partial pressure of hydrogen in the reaction zone of from about 30 to about 300 lbs/sq. in. A hydrogen partial pressure of 45 to 150 lbs/sq. in. is usually more desirable. Total pressure in the aromatization stage does not appear to be critical and may be from about 50 to about 500 lbs./sq. in. gauge, usually from about 100 to 4001bs./sq. in.

It is desirable and generally is necessary for enhanced efficiency of a vanadium oxide-alumina catalyst to maintain sulfur (as hydrogen sulnde, for example) in the .reaction zone so that when equilibrium'is reached between vanadium oxide of the catalyst and sulfur under the conditions prevailing, a mixture of vanadium oxide and vanadium sulde results and the atomic ratio afvanadiurn to sulfur in the catalyst lies within the range of from about 14:1 to about 2:1. This equilibrium may be maintained by a concentration of 1% or more by weight of sulfur in the hyl drocarbon feed, or by maintaining in the zone of reaction a partial pressure of hydrogen sulfide between about 0.5 and about 30 lbs/sq. in.

In the aromatization of a wide variety of petroleum fractions falling in the gasoline or naphtha ranges it has been found that a degree of dilution with a coke-suppressing gas, necessary for best results is provided by recycling gas produced during the aromatization reaction. 'Ihis gas contains hydrogen usually together with C3 or lighter hydrocarbons. The extent or volume of recycle in such a process desirably is from about 2000 to 12,000 cu. ft. (measured under standard conditions of temperature and pressure) per barrel of liquid hydrocarbon feed. This quantity of recycle gas provides from about 2 to about 14 diluent molecules for each reactant hydrocarbon molecule and decreases coke formation on the catalyst. Higher ratios may be employed but substantially lower ratios increase rapidly loss of feed to coke and gas.

Thus hydrocarbon feed admitted through line I0 of Figure 1 is passed through aromatization zone Il under conditions and in contact with a catalyst such as the foregoing. 'Ihe aromatized reaction products then flow by way of line I2 to an initial separation stage I3. In this initial separation stage the reaction products are fractionated by any suitable process such as a series of fractional distillations to yield at line IB what may be termed a heart cut consisting essentially of an equilibrium mixture of di-alkyl benzenes formed in the aromatization stage.

The overhead and the bottoms from this initial separation may be split in various ways. Preferably, a gas fraction comprising hydrogen, hydrogen sulfide and lighter than C5 hydrocarbons is removed via line I 4 and a valuable volatile liquid aromatic fraction is separated through line I6. The foregoing gas or a suitable portion thereof desirably is recycled to the aromatization stage and the liquid aromatic fraction of line I6 may pass to storage and be used as an aromatic thinner or solvent for lacquers, or the like, as well as for other purposes. The bottoms from the initial separation are removed at I1 and may be utilized in various ways, one of which is by recycling to the aromatization zone where further conversion to more valuable hydrocarbons is effected.

The equilibrium di-alkyl benzene fraction above referred to is passed through line I8 to a super-fractionation stage I9 where phthalic anhydride inconvertible alkyl benzenes are separated non-destructively and removed at 2| as a valuable aviation gasoline blending agent having certain improved performance characteristics as compared with the equilibrium di-alkyl benzene mixture. Phthalic anhydride convertible hydrocarbons are concentrated in the alkyl benzene residue which flows through line 22 to a catalytic vapor phase partial oxidation unit 23.

As previously noted, it'is important for best reai'raooa tion of phthalic anhydride inconvertiblehydrcx drocarbons are concentrated.` By proper correlation and control of these stages togetherl with feed stock and aromatization conditions it is possible, though usually not preferable, to produce a dialkyl benzene residue in the super-fractionation unit which is substantially 100% phthalic anhydride convertible. From about to about v20% phthalic anhydride inconvertible hydrocarbons carbons and preparation of an alkyl benzene -iesi-l due in which phthalic anhydride convertible hynormally are desired in the alkyl benzene residue I to obtain the benefits of a two-stage separation,

i. e., separation of phthalic anhydride inconvertible alkyl benzenes by a combination of non-destructive super-fractionation with destructive dium oxide as an active component is preferred.

The following paragraphs describe an exemplary process particularly adapted to partial oxidation of the foregoing di-alkyl benzene residues containing minor proportions of phthalic anhydride inconvertible hydrocarbons. i In oxidation unit 23 the alkyl benzene residu is vaporized and mixed with an excess of an oxygen-containing gas such as air and the hydrocarbon oxygen mixture contacted at elevated tem-` peratures with a vanadium oxide catalyst. The oxidation reaction which occurs in the catalyst zone is exothermic, and heat is removed by any suitable means to control temperature of the reaction. Catalyst temperature preferably is maintained in the zone of red heat. Such relatively'high temperatures together with a high izedA in 'the process.- Air is preferred although' mixtures of oxygen or air with nitrogen, carbon dioxide or other inert or non-oxidizing gases may be utilized. lDesirably the molar ratio of air to hydrocarbon should be at least about :1, andV preferably from 50:1 to 150:1. A still higher air to hydrocarbon ratio (300:1 or more) may be utilized with an adequate system for recovering the product in the resulting more dilute gaseous mixture.

The selective over-oxidation of phthalic aii-A hydride inconvertible alkyl benzenes in the abovedescribed process at least partially destroys these compounds and converts them into oxidation products which, for the m'ost part at least, are separable with relative ease from the phthalic anhydride contained inthe combustion gases. The over-oxidation of these hydrocarbons thus simultaneously serves to supply heat to maintain the catalyst at desired temperatures and to eect a destructive elimination of impurities which are removable, if at all, only with substantial difficulty by methods known to applicants. Thus,` when an alkyl benzene residuecontaining about 85 parts of phthalic anhydride convertible alkyl benzenes and about 15 parts phthalicV anhydride inconvertible hydrocarbons is utilized in theA oxidation stage, the inconvertible hydrocarbons are selectively over-oxidized mainly to carbon dioxide' and water, whereby these impurities are eliminated and phthalic anhydride easily separated by mere cooling and condensation of the combustion gases to yield a product containing no more than about 2% and even less than 1% aromatic impurities.

For example, the phthalic anhydride may be recovered in stage 24 by passing the hydrocarbon combustion mixture from the oxidation zone 'to' relatively large air-cooled chambers where the temperature of the gaseous mixture is reduced to below the phthalic anhydride frost point (i. e., the temperature at which phthalic anhydride condenses as a solid), whereby the anhydride solidifies as crystals in the cooling chamber. These crystals are collected and separated from the over-oxidized products of the phthalic anhydride inconvertible hydrocarbons as well as excess of oxygen-containing gas serve to form.

phthalicanhydride quickly and to destructively remove phthalic anhydride inconvertible benzenes by selective over-oxidation not only to the point of ring rupture but usually at least in major part to carbon dioxide and water. This selective over-oxidation serves to aid final purification and removal of the phthalic anhydride inconvertible compounds. The selective over-oxidation may be carried only to the point of ring rupture, and catalyst temperatures as low as about 800 F. are operable. However, a catalysttemperature in the dark red heat range is desirable, and from a dark blood red to a dark cherry red, as indicated in Marks Chemical Engineers Handbook (second edition, page 297), is preferred, i. e., about 990 F. to 1175 F. The entire catalyst bed need not be maintained at this high temperature .level since only a relatively short zone suicient to insure selective over-oxidation at least to ring rupture and preferably substantially completely to carbon dioxide and water need be in the dark red heat range (e. g., one-sixth t'o one-third of the catalyst bed). The temperatures referred to above are catalyst temperatures as measured by a thermocouple in the catalyst bed.

A large molar excess of oxidizing gas is utilfrom other combustion products. The recovery of phthalic anhydride from the combustion gases and separation from the over-'oxidized products may be accomplished in various ways including washing the mixture of gases with a suitable solvent or chemical reactants or by selective absorption. However, the best method at present appears to be cooling and condensation as above described.

Reference has been made above to metal oxide catalysts for partial oxidation of alkyl benzenes and to aromatization catalysts for conversion of non-aromatic' to aromatic hydrocarbons. Although various catalysts of these types are known, a more detailed discussion and description will be given to guide those skilled in the art in the practice of this invention.

Aromatzzation cataZysts.-Preferred aromatization catalysts consist of minor molar proportions of oxides of the transition metals of the VI (e. g., chromium or molybdenum), V (e. g., vanadium) and IV (e. g., titanium and cerium) Groups of the Periodic System supported on carriers of relatively low catalytic activity such as specially prepared alumina or magnesia. Substances having no unfavorable reaction with the catalytic metal oxides and providing a stable large surface may be used as carriers. Within the broader aspects from aqueous or other solutions.

of preparation are to use such a procedure and such compounds of the catalytic metal as will finally leave only the oxides oi the desired metal or metals on the particles of the support without interfering constituents. Such compounds usually are water-soluble metal nitrates or ammonium salts of the metallic acid. Specific examples of suitable catalystcombinations for aromatization are vanadium oxide-alumina, molybdenum oxidealumlna,'and chromium oxide-alumina, in which the aluminay is the supporting matrix. Various combinations of the catalytic oxides on a suitable support such as alumina are useful, e. g., chromium oxide-molybdenum oxide, vanadium oxide-molybdenum oxide, vanadium' oxide-chromium oxide, vanadium oxide-chromium oxide-molybdenum oxide, each on alumina. Other catalytically active oxides are tungsten oxide, zinc oxide and certain mixed oxides and sulildes of the foregoing metals.

Preferred catalysts for aromatizing naphthenic petroleum hydrocarbons are the molybdenum oxide-alumina and vanadium' oxide-alumina catalysts. More particularly, the presently preferred catalysts of this type are those obtained by coprecipitation of the oxides to yield an interlocked oxide of gel structure.

In preparing the foregoing co-precipitated catalysts the aluminum component may be supplied from soluble salts` such as aluminum chloride, aluminum acetate or aluminum nitrate. Taking aluminum chloride as typical, an aqueous solution containing about 6% aluminum chloride by weight is suitable though solutions containing from about .05 to about 2.5 lbs/gal. are suitable under certain conditions. The molybdenum' or vanadium component may be supplied from a solution of ammonium molybdate or ammonium vanadate. Taking molybdenum as an example, ammonium di-molybdate (NH4)2M004, or amammonium heptamolybdate (NH4ieMo'1Oz4, as most convenient, may be utilized as the source of the molybdenum component. If these ammonium salts are not available as such, a satisfactory solution for use in preparing the preferred catalyst may be had by dissolving either molybdic acid or molybdic anhydride in an appropriate quantity of aqueous ammonia. When the heptamolybdate is employed it has been found that most satisfactory results are obtained at about 1.6 lbs/gal. of solution though solutions ranging from 2 to 8 lbs/gal. may sometimes be employed.

It has been determined that the substantial absence of any alkali metal component, and particularly of a sodium component, from the coprecipitated catalyst is essential in order that the catalyst may have maximum activity and maxi-u mum life. A satisfactory procedure for precipitating the catalyst components is to first mix aqueous ammonia containing from about 10 to NH3 with the molybdenum salt solution and then to add this mixture to the aluminum chloride solution or to add the aluminum chloride solution to the mixture. It has beenffound that during this precipitation the reaction mixture should have a pH of from about '1.25 to about 8 at the conclusion of the precipitating step, i. e., when aluminum chloride is added to the mixture of ammonia and ammoniu'm molybdate solutions The principles 14 this addition should be stopped before the pH of the reaction mixture is reduced below the above limits. Conversely, when the mixture of ammonium molybdate and ammonium solutions is added to the aluminum chloride solution, this addition should be continued luntil the pH of the reaction mixture is raised to the above-indicated alkaline side.

The precipitate thus obtained is a thoroughly homogeneous ilocculent mass or weak gel which e is readily collected and broken up for further procwashed gel is then dried, powdered, and may be mixed with from about 1% to 10% of graphite or other suitable lubricant. This dried powder containing the desired lubricant is next compressed into pellets by means of any suitable tablet or pill machine and subjected to a final calcining step. The temperature of calcining may be conveniently about 1100 F. or above. A preferred calcining procedure comprises slowheating for about 3 hours and until a temperature of about 1100 F. is reached, followed by at least 2 hours heating at a temperature of from 800 to 1300u F. The pellets may be calcined at this elevated temperature for periods as long as 150 hours or more. This calcining treatment removes aluminum chloride and water but not the graphite.

A catalyst suitable for aromatization of parafiinic hydrocarbons by dehydrocyclization may be prepared by impregnating granulated activated alumina with an aqueous solution of chromium trioxide to yield 8% chromium sesquioxide on the alumina. Grade A activated alumina sold by the Aluminum Corporation of America is suitable. The impregnated particles are dried and preferably reduced in situ in an atmosphere of hydrogen before use.

Oxidation catalyst-Various metal oxides have been used as a catalyst for the partial oxidation of aromatic hydrocarbons to phthalic anhydride or the like. Such catalysts include the oxides of vanadium, molybdenum, mixed oxides from tin vanadate. and mixed vanadium-molybdenum 'SultS.

, a catalyst in which catalytic action takes place in or on the outer surface region rather than in the deeper interior portion of a macroscopic catalyst granule, pellet, or the like. Poro us catalysts, though not precluded, have been found less effective and tend to increase over-oxidation of the phthalic anhydride convertible alkyl benzenes together with the phthalic anhydride inconvertible components. To the extent this occurs, advantages to be derived from the two-stage purification procedure are defeated.

A specific example of a preferred type oxidation catalyst may be prepared by evaporating an aqueous paste of chemically pure ammonia metavanadate on 20 mesh granular aluminum and igniting the coated granules at 1200 F. to liberate ammonia and form vanadium oxide which fuses the granules into a coherent mass.

The fused mass is broken and screened to pass a- 14 mesh and be retained on a 30 mesh screen. A catalyst prepared in a similar manner but containing 60%g vanadium' oxide, 30% molybdenum oxide and manganese oxide on 20 mesh aluminum is also suitable. Likewise, other catalyst supports may be substituted for thelaluminum; for example, silicon carbide or other inert high melting oxidation resistant granular materials.

In connection with the processes of Figures 2 and 3, it should be observed that treatment of two principal specictypes of feed stocks are and in Figure 3 the feed stock has an end point v substantially higher than the 250 F. initial boiling point of the equilibrium mixture to be superfractionated. It has been found that when the original feed stock contains more than about 60 non-aromatics and has ,an end point more than about A F. above the initial boiling point of the equilibrium mixture to be super-fractionated, simple fractional distillation does not suffice for initial separation and preparation of the equilibrium alkyl benzenes.

The process of Figure 2 embraces additional features encompassed bythe present invention and involves correlation of process steps with particular hydrocarbon stocks and aromatization conditions to give high yields of desired products. More particularly, the process here shown ihvolves the major process stages of aromatization, initial separation of the aromatized reaction products by simple fractional distillation to yield an equilibrium mixtureof alkylbenzenes of selected boiling range, super-fractionation of the equilibrium mixture to concentrate phthalic anhydride' convertible alkyl benzenes in a distillation residue, vapor phase partial oxidation of the alkyl benzene residue, and recovery of phthalic anhydride product from the reaction gases.

In this second embodiment of the invention a straight-run highly naphthenic petroleum fraction (e. g. from Kettleman Hills crude oil) boiling within the range from about 230 to 275 F. is fed through I line 26 to aromatization zone 21 where the hydrocarbons are aromatized with the catalyst and under conditions disclosed in the description of the corresponding aromatization step of Figure 1. The reaction product from the aromatization zone flows by line 28 to stripper 29 where recycle gas is-removed and returned to the aromatization stage by way of line 3|. The stripped hydrocarbon reaction product is fractionated by distillation at 32 and low-boiling liquids from Cs to about 275 F. end point are removed as distillation overhead. Bottoms from this distillation stage are again fractionated in column 33 and. equilibriumaromatic boiling within the range'from about 275 to about 295 F. lare removed as overhead. Bottoms from fractionator 33 boiling from 295 F. furnish a heavy recycle stock which may be returned to aromatization zone 21 by way of line 34.

With the foregoing selection of boiling ranges, feed stock, aromatization conditions, and by distillation through ordinary fractionation columns (e. g. 45 theoretical plates or better), equilibrium aromatics containing less than about nonaromatic hydrocarbons may be obtained. It is important that these equilibrium aromatics flowing from fractionator 33 via line 36 to superfractionator 31 contain no more thanabout 25% non-aromatica Non-destructive separation of al major proportionl of phthalic anhydride inconvertibl'e aromatics may then be effected insuperfractionator 31 by removing as 'overhead .hydrocarbons boiling from about 275 toabout 285 F. This overhead .fraction comprises a mixture of alkyl benzenes having highanti-knock and exceptional value as an aviation gasoline blending stock where high rich rating is required. The super-fractionation preferably is effected in a distillation column having the equivalent of `at least about 45 theoretical plates and by utilizing a reflux ratio on distillate of from about 7:1 to' 12:1. Very" close control is required for elcient separation asl Ipreviously described.

Residual alkyl benzenes boiling within vthe A range from about-285 to 295 F. comprise an excellent phthalic anhydride conversion stock which flows from super-fractionator 31 by way of line 38 to vapor phase catalytic converter 39. This conversion stock'preferably contains from about 5 to about 20% phthalic anhydride inconvertible hydrocarbons and is subjected to catalytic vapor phase partial oxidation under the conditions and preferably with a vanadium oxide catalyst such as described in the corresponding process stage of Figure 1. The phthalic anhydride inconvertible`alkyl benzenes are destructively oxidized and removed in the phthalic anhydride recovery stage 4| by cooling the combustion gases to selectively precipitate `or condense the phthalic anhydrlde product while removing, as gases, oxidation products of the destroyed alkyl benzenes.

A third embodiment of the invention is illustrated in the process of Figure 3 and involves the major steps of aromatization, initial separation of the aromatized reaction product by simple fractionation to yield an aromatic heart cut of selected boiling range, reduction of the nonaromatic content of said heart cut, superfractionation of a resulting alkyl benzene mixture to concentrate phthalic anhydride convertible alkyl benzenes in a distillation residue, vapor phase partial oxidation of the residue Aand recovery of phthalic anhydride from the reaction valve controlled inlet line 46 to aromatization .4

zone 41 where the hydrocarbons are aromatized with a catalyst and under conditions such as disclosed in the corresponding .aromatization step of Figure 1. The reaction product from the aromatization zone flows by way of line 48 to stripper 49 where recycle gas is removed and returned to the aromatization stage by way of line 5I. The stripped hydrocarbon reaction product is fractionated by distillation at 52 and low boiling liquids from Cs lto about 250 F. end point are removed as distillation overhead through line 53. 4Bottoms from this distillation stage are again fractionated in column 54 and an aromatic fraction or heart cut boiling within the range of from about 250. to about 300 F. is removed as overhead. This laromatic fraction or heart cut" may now either by way of valve controlled line 56 to storage 51 or preferably through valve controlled line 58 to converter 59. Bottoms from fractonator 54 boiling above about 300 F. furnish a heavy recycle stock which may be returned to aromatization zone 41 by way of line 6 I.

When overhead from fractionator 54 is diverted to storage 51, the stored hydrocarbon stock is accumulated and finally re-run through aromatization zone 41 independently of and separately from naphthenic feed from line 46. The re-run stock is again subjected to stripping at 49, fractionation at '52 and 54 to yield an equilibrium alkyl benzene mixture which is then subjected to super-fractionation, vapor phase oxidation, and recovery of product as described in connection with Figure 1 of the drawing. This batchwise operation is, however, not a preferred procedure except where equipment limitations require it.

In continuous operation, the original 250 to 300 F. heart cut from fractionator 54 is treated in converter 59 to reduce the non-aromatic content of the selected hydrocarbon fraction. As previously indicated, this reduction` may be effected by selective solvent extraction processes, by selective cracking or by subjecting the said hydrocarbon fraction to a second aromatization treatment whereby the non-aromatic hydrocarbons are converted either to aromatics or low boiling hydrocarbons, or both. The latter preferred treatment is illustrated in the process here shown. A suitable and preferred aromatization treatment comprises process conditions such as disclosed in connection with the aromatization stage of Figure 1; for example, treatment with a molybdenum-alumina catalyst at about 900- l100 F. and a space rate corresponding to from about 0.1 to 2.0 volumes of liquid hydrocarbon fraction per volume of catalyst per hour in the presence of from about 2000 to 12,000 cubic feet of a recycle gas per liquid barrel of feed, said recycle gas containing approximately to 70% hydrogen. More specifically, one suitable treatment comprises passing one volume of liquid hydrocarbon per volume of catalyst per hour at a total pressure of 200 pounds per square inch with 6000 cubic feet of recycle gas per barrel of feed and themolybdenum-alumina catalyst specifically described hereinabove.

When utilizing conditions in aromatization zone 41, corresponding to those described in connection with Figure 1 of the drawing together with fractionation as above indicated, the feed to converter 59 will usually contain about 50 to about 75% aromatics of which only about 25% are phthalic anhydride convertible. After treatment in converter 59 and simple fractionation as subsequently described herein, a 275 to 295 F. equilibrium mixture of alkyl benzenes will be substantially free of non-aromatics and contain about phthalic anhydride convertible hydrocarbons. Alternatively, by selecting a 285 to 300 F. fraction as overhead from fractionator 54 and feeding the same to converter 58, an alkyl benzene cut may then be obtained which contains from about to 65/% phthalic anhydride convertible hydrocarbons. This latter procedure, however,

involves some sacriiice of over-all yield of other 66 then pass to fractionator 58 and an equilibrium the phthalic anhydride inconvertible aromatics.

This treatment may be effected in super-fractionator 1I by removing. as overhead, hydrocarbons boiling from about 270 to 285 F. The super-fractionator is operated substantially as in processes previously described herein. The residual alkyl benzenes boiling within the range of from about 285 to 295 F. flow from super-fractionator 1| by way of line 12 to the partial oxidation stage 13 and phthalic anhydride recovery stage 14 of the process which may be substantially the same as those previously described herein.

If desired, it is possible to feed a paraii'inic or olenic petroleum fraction to the aromatization stage 41 of Figure 3. Likewise, mixed parafiinnaphthene base petroleum fractions may be utilized. With particular feed stocks, it will be found advantageous to adopt catalysts and process conditions in stage 41 particularly useful in dehydrocyclization reactions. Such processes and catalysts are exemplified by the chromium oxidealumina catalyst previously described and by process conditions such as a temperature of about 875 F. and a space rate of about 0.3 volumes of feed per volume of catalyst per hour. The feed stock in such a process may be predominantly octanes, including normal octane and 2,5-dimethyl hexane.

Although this invention has been illustrated with various specific embodiments and preferred process conditions have been described, numerous alterations utilizing the principles thereof will occur to those skilled in the art, and it is to be understood that the invention may be otherwise embodied or practiced within the scope of the appended claims.

We claim:

l. In a process of producing phthalic anhydride and an improved hydrocarbon stock having enhanced properties as a blending agent in aviation gasolines, the steps which comprise treating an aromatized mixture of petroleum hydrocarbons consisting essentially of an equilibrium mixture of alkyl benzenes boiling within the range of from about 250 to about 300 F. to separate an alkyl benzene fraction boiling within the range of from about 275 to about 285 F. and an alkyl benzene fraction boiling within the range of 285 to about 300 F., said 275-285 F. fraction of alkyl benzenes being characterized by an aviation gasoline blending action superior to that of said equilibrium mixture of alkyl benzenes and said 285-300 F.

alkyl benzene fraction containing at least about 70% by volume oi' phthalic anhydride convertible alkyl benzenes, oxidizing said last alkyl benzene fraction to phthalic anhydride and over-oxidizing inconvertible hydrocarbons therein at least to the point of ring rupture by passing said last fraction in vapor phase over a vanadium oxide catalyst at a catalyst temperature of from 800 F. to l175 F. and separating said phthalic anhydride from said over-oxidized components.

2. A process of producing phthalic anhydride which comprises feeding to an aromatizing zone a petroleum fraction boiling within the range of from about 180 F. to about 420 F., said petroleum fraction comprising aromatizable naphthenic petroleum hydrocarbons, contacting said feed with a hydrogenation-dehydrogenation catalyst in said aromatization zone under dehydrogenation conditions whereby non-aromatic hydrocarbons in said feed are converted to alkyl benzenes, fractionating said reaction mixture to separate therefrom an aromatic cut comprising mixed alkyl benzenes and consisting at least predominantly of a mixture of phthalic anhydride inconvertible with a minor proportion of phthalic anhydride convertible aromatic hydrocarbons, non-destructively eliminating a major portion of the phthalic anhydride inconvertible aromatic hydrocarbons from said aromatic cut by fractionating said aromatic cut to separate a mixed alkyl benzene fraction boiling Within the range of from about 285 F. to about 300 F. and containing a residual minor proportion of phthalic anhydride inconvertible with a major proportion of phthalic anhydride convertible alkyl benzenes, converting alkyl benzenes'of said last fraction to phthalic anhydrideby vapor phase oxidation in a phthalic anhydride forming zone with a vanadium oxide catalyst at phthalic anhydride forming temperatures, eliminating said residual phthalic anhydride inconvertible alkyl benzenes by combustion to products readily separable from the phthalic anhydride by concurrently over-oxidizing said phthalic anhydride inconvertible alkyl benzenes at least to the point of ring rupture by vapor phase oxidation with a vanadium oxide catalyst in said phthalic anhydride forming zone, passing said vapor phase oxidation products from said phthalic anhydride forming zone to a cooling zone, separating said phthalic anhydride from said gaseous over-oxidation products by crystallization of phthalic anhydride in said cooling zone, and removing residual ring-rupture impurities condensed with the phthalic anhydride in the cooling zone by distillation of the crystallized phthalic anhydride.

3. A process as dened in claim 2, wherein oxidation in said phthalic anhydride forming zone is eiected at a catalyst temperature of from about 800 F. to about 1175 F.

4. A process as dened in claim 2, wherein said vanadium oxide catalyst is a non-porous catalyst.

5. Aprocess of producing phthalic anhydride which comprises feeding to an aromatizing zone a petroleum fraction boiling within the range of from about 180 F. to about 420 F., said petroleum fraction comprising aromatizable naphthenic petroleum hydrocarbons, contacting said feed with a hydrogenation-dehydrogenation catalyst in said aromatization zone under dehydrogenation conditions whereby non-aromatic hydrocarbons in said feed are converted to alkyl benzenes, fractionating said reaction mixture to separate therefrom an aromatic cut comprising mixed alkyl benzenes and consisting at least predominantly oi a mixture of phthalic anhydride inconvertible with a minor proportion of phthalic anhydride convertible aromatic hydrocarbons, non-destructively eliminating a major portion of the phthalic anhydride incovertible aromatic hydrocarbons from said aromatic cut by fractionating said aromatic cut to separate a mixed alkyl benzene fraction boiling within the range of from about 285 F. to about 300 F. and containing from about 3% to about 30% phthalic anhydride inconvertible hydrocarbons with from about 97% to about '70 phthalic anhydride convertible alkyl benzenes, oxidizing said last alkyl benzene fraction to phthalic anhydride and concurrently selectively over-oxidizing said phthalic anhydride inconvertible hydrocarbons at least to the point of ring rupture by passing said fraction in vapor phase over a vanadium oxide catalyst at a catalyst temperature of from 800 F. to 1175 F., and separating said phthalic anhydride from said overoxidized components.

6. A process as dened in claim 5, wherein said vapor phase oxidation is eiected at a catalyst temperature of from about 990 F. to about 1175 F.

'7. A process of producing phthalic anhydride from a petroleum naphthenic hydrocarbon fraction boiling below about 320 F. and containing naphthenic hydrocarbons boiling above about 250 F., which comprises contacting said petroleum fraction with a hydrogenation-dehydrogenation catalyst in an aromatization zone under dehydrogenation conditions, whereby naphthenic hydrocarbons in said fraction are converted to alkyl benzenes, initially fractionating the resulting reaction mixture to separate an aromatic cut boiling within the range of from about 250 F. to about 300 F. and consisting at least predominantly of a mixture of phthalic anhydride inconvertible with a minor proportion of phthalic anhydride convertible aromatic hydrocarbons boiling within the range of from about 250 F. to about 300 F., non-destructively removing from said aromatic cut a major proportion of phthalic anhydride inconvertible hydrocarbons by fractionally distilling overhead an alkyl benzene cut boiling below about 285 F. to leave an alkyl benzene residue boiling from about 285 F. to about 295 F.,

said residue consisting essentially of a major proportion of phthalic anhydride convertible alkyl benzenes with a minor proportion of phthalic anhydride inconvertible alkyl benzenes, converting alkyl benzenes of said residue to phthalic anhydride by vapor phase oxidation in a phthalic anhydride forming zone with a vanadium oxide catalyst at a catalyst temperature of from about 800 F. to about 11'75" F., and eliminating phthalic anhydride inconvertible alkyl benzenes in said residue by combustion to products readily separable from the phthalic anhydride by concurrently overoxidizing said phthalic anhydride inconvertible alkyl benzenes at least to the point of ring rupture by vapor phase oxidation in said phthalic' anhydride forming zone.

8. A process of producing phthalic anhydride from a straight run naphthenic petroleum iraction containing naphthenic hydrocarbons boiling above about 200 F. and below about 320 F.,

which comprises contacting said petroleum fracv tion with a hydrogenation-dehydrogenation catalyst in' an aromatization zone under dehydrogenation conditions whereby naphthenic hydrocarbons in said fraction are converted to alkyl benzenes, initially fractionating the resulting reaction mixture to separate an aromatic cut boiling within the range of from about 250 F. to about 300 F. and consisting at least predominantly of a mixture of phthalic anhydride inconvertible with a minor proportion of phthalic anhydride convertible aromatic hydrocarbons, non-destructively removing from said aromatic cut a major proportion of phthalic anhydride inconvertible hydrocarbons by fractlonally distilling overhead an alkyl benzene cut boiling below about 280 F. to leave an alkyl benzene residue boiling from about 225 to about 295 F., said residue consisting essentially of a major proportion of phthalic anhydride convertible alkyl benzenes with a minor proportion of phthalic anhydride inconvertible alkyl benzenes, converting alkyl benzenes of said residue to phthalic anhydride by vapor phase oxidation in a phthalic anhydride forming zone with a vanadium oxide catalyst at a catalyst temperature of from about 800 F. to about l175 F., and eliminating phthalic anhydride inconvertible alkyl benzenes in said residue by combustion to products readily separable from the phthalic anhydride by concurrently overoxidizing said phthalic anhydride inconvertible alkyl benzcnes at least. to the point of ring rupture by vapor phase oxidation in said phthalic anhydride formingT zone.

9. A process of producing phthalic anhydride and an improved hydrocarbon stock having enhanced properties as a blending agent in aviation gasoline, from an aromatized petroleum fraction boiling within the range of from about 250 F. to about 300 F. and comprising an alkyl benzene mixture containing at least of non-aromatic petroleum hydrocarbons which boil Within the range of said alkyl benzene mixture and thereby interfere with separation of said alkyl benzene components of the mixture, said process comprising contacting said petroleum fraction with a hydrogenation-dehydrogenation catalyst under dehydrogenating conditions whereby the boiling range of said non-aromatic hydrocarbons is modied, initially fractionating from the resulting reaction mixture a first alkyl benzene fraction boiling within the range of from about 275 F. to about 300 F., separating said rst alkyl benzene fraction by fractional distillation into a second alkyl benzene fraction boiling within the range of from about 275 F. to about 285 F., and a third alkyl benzene fraction boiling within the range of from about 285 F. to about 300 F., said second alkyl benzene fraction being characterized by an aviation gasoline blending action superior to that of said original petroleum fraction, and said third alkyl benzene fraction containing at least about 70% by volume of phthalic anhydride convertible alkyl benzenes together with from about 3% to about 30% by volume of phthalic anhydride inconvertible alkyl benzenes, oxidizing said third alkyl benzene fraction to phthallc anhydride and concurrently selectively over-oxidizing phthalic anhydride inconvertible hydrocarbons in said third fraction at least to the point of ring rupture by passing said third fraction in vapor phase over a vanadium oxide catalyst at a catalyst temperature of from 990 F. to 1 175 F., and separating said phthalic anhydride from over-oxidized components.

10. A process which comprises producingfrom petroleum a hydrocarbon fraction containing from 70% to 97% oi alkyl benzenes or a type convertible by direct oxidation to phthalic anhydride and an alkyl benzene hydrocarbon stock having enhanced properties as a blending agent in aviation gasolines; said process comprising feeding to an aromatizing zone a naphthenic petroleum fraction boiling Within the range of from about 180 F. to about 420 F., said petroleum fraction containing aromatizable naphthenic hydrocarbons and having an end point at least about 10 F. above the initial boiling point of a iirst alkyl benzene hydrocarbon fraction referred to hereinafter, contacting said petroleum feed with a hydrogenation-dehydrogenation catalyst in said aromatization zone under dehydrogenation conditions whereby non-aromatic hydrocarbons in said feed are converted to alkyl benzenes, separating from the reaction products a rst alkyl benzene hydrocarbon fraction boiling within the range of from about 250 to about 300 F. and having a non-aromatic hydrocarbon content of less than about 15%, the aromatic hydrocarbon content of said first alkyl benzene hydrocarbon fraction being predominantly a mixture of phthalic anhydride inconvertible with a minor proportion of phthalic anhydride convertible alkyl benzenes, fractionally distilling from said first alkyl benzene fraction a second alkyl benzene fraction boiling below 285 F. and a third alkyl benzene fraction boiling within the range of from about 285-300 F., said second alkyl benzene fraction being characterized by an aviation gasoline blending value superior to that of said first alkyl benzene mixture and said third fraction containing from about 3% to about 30% of phthalic anhydride inconvertible components and from about to 97% of phthalic anhydride convertible alkyl benzene.

IRVING E. LEVINE.

WILLIAM H. CLAUSSEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,324,715 Andrews Dec. 9, 1919 2,294,130 Porter Aug. 25, 1942 2,345,600 Heard et al. Apr. 4, 1944 2,380,279 Weltz, Jr. July 10, 1945 2,383,072 Oblad Aug. 21, 1945 2,396,761 Tilton Mar. 19, 1946 2,398,526 Greenburg Apr. 16, 1946 2,404,902 Claussen et al July 30, 1946 2,416,350 Rollman Feb. 25, 1947 2,438,369 Levine Mar. 23, 1948 OTHER REFERENCES Zelinsky et al., Jour. Ind. Eng. Chem., vol. 27, 1209-11 (1935). 

